Effect of lime on the mechanical response of a soil for use in unpaved forest roads

Abstract

The main objective of this study was to propose the application of soil-lime mixtures asa primary coating layerof unpavedforestroads based on the premise that this layer can be considered mechanically similar to a flexible pavementsub base layer, aiming to fill a gap in the current technical literature and engineering practice in this field of knowledge. In the study, a laboratory test program was carried out in a residual gneiss soil encompassing: (i) geotechnical characterization tests; (ii) compaction tests at the standard Proctor energy on soil specimens and on soil-lime mixturespecimens prepared with lime contents of 2, 4 and 6% related to the dry soil mass; (iii) unconfined compressive strength tests on soil specimens compacted at the standard Proctor optimum parameters; and (iv) unconfined compressive strength tests on specimens of soil-lime mixtures compacted at the standard Proctor optimum compaction parameters with lime contents of 2, 4 and 6%, and cured at 22.8°C in the curing periods of 3, 7, 28 and 90 days. The results showed that the addition of lime resulted in: (i) reduction in soil maximum dry unit weight (g_dmax) and increase in soil optimum water content (w_opt);and(ii) significant gains in soil unconfined compressive strength that evidenced the expressive occurrence of pozzolanic reactions in the mixtures.Based on the hypothesis of a similar requirement for soil-cement and soil-lime mixtures, the tested soil-lime mixtures met the minimum mechanical strength (1.2MPa) required for application as a primary coating layer of unpaved forest roads.